This invention relates generally to chair bases and chair height adjustment mechanisms. In particular, the invention is directed to a reliable and inexpensive chair base and height adjusting mechanism of the type that is automatically adjustable by rotation of the chair whenever the chair is unoccupied.
A number of different arrangements have been provided to enable the user of a swivel chair to selectively adjust the height of a chair. The most prevalent prior art designs employ a threaded spindle and nut combination that is vertically adjustable on a floor engaging base. In earlier mechanisms the nut is permanently fixed relative to the floor engaging base so that rotation of the chair seat and its spindle produces a raising or lowering of the spindle and chair seat. The disadvantages of such a construction are apparent since it follows that whenever the chair seat is swivelled, either intentionally or accidentally, the height of the chair seat is altered.
Another arrangement involves the use of a floating spindle nut which precludes vertical displacement of the spindle except when the user manually engages the nut and positively rotates the nut or the seat to raise or lower the spindle extending therethrough. This arrangement is inconvenient since the user must reach under the seat and manually hold or turn the nut relative to the spindle. Other disadvantages common to both of these related forms of chair height adjusting mechanisms include limited adjustment ranges and the fact that the threaded spindle and spindle nut are costly to machine and must be lubricated. The lubricated spindle and nut are exposed to the collection of dirt, dust and lint which further impede manual adjustment of the chair, often soil the user of the chair, and in general detract from the aesthetic appearance of the chair.
Numerous alternatives to this traditional type of chair adjustment arrangement have been suggested in the prior art. These arrangements include telescoping tubular columns wherein height adjustment is effected by a hand lever engaging or disengaging slots, balls, wedging washers, garter springs, or expanding collars to effect height adjustment of the telescoping tubular columns. Gas cylinders and hand operated pumps have also been employed. Of all of these alternative designs, the most appealing from the users point of view is a type of automatic chair height adjusting mechanism that engages whenever the chair is unoccupied. With this type of chair height adjustment mechanism the chair seat may be vertically adjusted by simple rotation of the unoccupied chair. When the chair is occupied the chair adjustment mechanism automatically disengages to allow the chair to freely rotate without vertical adjustment. However, this type of automatic chair height adjusting mechanism, along with the other alternative designs tend to be complex and costly to manufacture.